Method for coating steel plate with metal and metal-coated steel plate manufactured using same

ABSTRACT

Provided are a method for coating a steel plate with a metal and a metal-coated steel plate manufactured by the method. The method includes: heating powder of a first metal at a temperature lower than a softening temperature; heating a gas to a temperature of 200° C. to 600° C.; vacuum-ejecting the heated first metal powder together with the heated gas to form a metal coating layer; and forming a plating layer of a second metal on the metal coating layer.

TECHNICAL FIELD

The present disclosure relates to a method for coating a steel platewith a metal and a metal-coated steel plate manufactured by the method,and more particularly, to a method of forming a pore-free coating layerby forming a porous coating layer through a vacuum ejection coatingprocess and then forming a plating layer, and a steel plate on which thepore-free coating layer is formed.

BACKGROUND ART

A method of coating with particles may be used as a surface treatmentmethod for coating various materials with various powder materials, andan ejection velocity is guaranteed by a gas pressure difference betweena powder carrier gas and a coating portion normally having a boundary ata nozzle. Particle coating refers to coating with particles, and sinceparticle coating is performed as particles having a size of several tensto several hundreds of nanometers (nm) collide with a coating targetmaterial, a coating layer is formed at a much higher rate than inphysical vapor deposition (PVD), chemical vapor deposition (CVD), or thelike in which coating is performed on an atomic or molecular basis. Inaddition, the chemical composition of a raw material powder is notchanged during the particle coating.

Examples of particle coating include a spraying method (such as athermal spraying method or a cold spraying method) and a vacuum ejectionmethod which are generally useful for coating with solid particles ofmetals, alloys, cermet, or the like, and in these methods, temperatureand ejection velocity are key factors.

In the vacuum ejection method, a coating unit is maintained in a vacuumstate (a low-pressure state) to create a pressure difference. That is, acoating target member is provided in a vacuum body, and coating isperformed by ejecting powder onto the coating target member in a statein which the powder is carried by a carrier gas. This method does notrequire that the carrier gas has a high pressure, thereby consuming asmaller amount of gas than the spraying method and enablingroom-temperature coating because it is not necessary to heat gas to ahigh pressure.

The possibility of mass production (coating efficiency) and economicalaspects (the amount of gas consumption) are considered to apply suchparticle coating methods to the steel industry, for example, for steelplate surface treatment. In this regard, although the vacuum ejectionmethod is economical because of a low amount of gas consumption, thevacuum ejection method results in low coating efficiency (stackingamount/total ejection amount) and is usable for limited coatingmaterials because of a coating temperature substantially close to roomtemperature and a lower powder particle ejection velocity than that ofthe spraying method (such as a thermal spraying method or a coldspraying method).

As disclosed in Korean Patent Application No. 2008-0076019, the vacuumejection method is generally used for coating with a brittle materialsuch as a ceramic material which is pulverized into powder andrecombined during coating and is not suitable for coating with a ductilematerial such as a metal requiring a large amount of energy for plasticdeformation.

In addition, although a particle coating method using the sprayingmethod (such as a thermal spraying method or a cold spraying method) hashigh efficiency in terms of metal powder, since a body in which acoating target member is provided is maintained at atmospheric pressure,high-pressure gas having a pressure of several megapascals (MPa) is usedas a powder carrier gas to create a large pressure difference fromatmospheric pressure, thereby resulting in a large amount of gasconsumption. In addition, expensive low-density gas such as He or N₂ iscommonly used to ensure a particle velocity for high-speed collisionswith a coating target member maintained at atmospheric pressure. Thatis, the spraying method is generally used for coating a small area andrequires particles having a size of several tens of micrometers (μm) forhigh-speed ejection due to air resistance at atmospheric pressure.Furthermore, according to the spraying method, it is necessary to form athick coating layer having a thickness within the range of several tensto several hundreds of micrometers (μm) because of problems such ascoating layer defects and residual stress, and thus it is practicallydifficult to form a dense thin coating layer having a thickness ofseveral micrometers (μm) to several tens of micrometers (μm) by thespraying method. In general, according to such particle coating methodsfor coating with metal powder, pores are formed in a coating layer, andparticularly, in the case of coating with a thin film having a thicknessof several micrometers (μm) to several tens of micrometers (μm),corrosion factors permeate through such pores, thereby lowering thecorrosion resistance of steel plates.

Therefore, if a coating method addressing the above-described problemswith the spraying method and the vacuum coating method is provided forforming a metal coating layer having maximized functionality, such ascorrosion resistance on a steel plate surface, the coating method willbe widely used in related fields.

DISCLOSURE Technical Problem

An aspect of the present disclosure may provide a method for coating asteel plate with a metal without pores.

An aspect of the present disclosure may also provide a metal-coatedsteel plate having a pore-free coating layer manufactured by the metalcoating method.

Technical Solution

According to an aspect of the present disclosure, a method for coating asteel plate with a metal may include: heating a first metal powder to atemperature equal to, or higher than, room temperature but lower than asoftening temperature; heating a gas to a temperature of 200° C. to 600°C.; vacuum-ejecting the first metal powder, having been heated, togetherwith the heated gas to form a porous first metal coating layer; andforming a plating layer of a second metal in gaps between powderparticles of the first metal coating layer.

The first metal may include at least one metal selected from the groupconsisting of copper (Cu), aluminum (Al), zinc (Zn), iron (Fe), nickel(Ni), chromium (Cr), molybdenum (Mo), titanium (Ti), cobalt (Co),manganese (Mn), tungsten (W), zirconium (Zr), and tin (Sn).

The first metal powder may have an average particle size of 1 μm to 20μm.

The gas may include at least one gas having a density equal to or lowerthan the density of air which is selected from the group consisting ofnitrogen (N₂), helium (He), and air.

The vacuum-ejecting may be performed at a pressure of 0.01 Torr to 20Torr.

The vacuum-ejecting may be performed at a temperature of 10° C. to 200°C.

The second metal may include at least one metal selected from the groupconsisting of zinc (Zn), nickel (Ni), tin (Sn), copper (Cu), andchromium (Cr).

The forming of the plating layer of the second metal may be performed byan electroplating method or an electroless plating method.

The method may further include polishing the plating layer of the secondmetal.

The method may further include performing a heat treatment process at atemperature of 200° C. to 1000° C. after the forming of the platinglayer of the second metal.

According to another aspect of the present disclosure, a metal-coatedsteel plate may be manufactured by the method of the aspect of thepresent disclosure.

According to another aspect of the present disclosure, a metal-coatedsteel plate may include: a steel plate; a porous first metal coatinglayer formed on at least one surface of the steel plate using a firstmetal powder; and a plating layer of a second metal formed in gapsbetween particles of the first metal powder of the first metal coatinglayer.

The second metal plating layer may be formed on a surface region of thefirst metal coating layer and in pores of the first metal coating layer.

An anchoring layer may be formed on an interface between the steel plateand the first metal coating layer.

The first metal may include at least one metal selected from the groupconsisting of copper (Cu), aluminum (Al), zinc (Zn), iron (Fe), nickel(Ni), chromium (Cr), molybdenum (Mo), titanium (Ti), cobalt (Co),manganese (Mn), tungsten (W), zirconium (Zr), and tin (Sn).

The first metal powder may have an average particle size of 1 μm to 20μm.

The second metal may include at least one metal selected from the groupconsisting of zinc (Zn), nickel (Ni), tin (Sn), copper (Cu), andchromium (Cr).

Advantageous Effects

According to the present disclosure, since heated gas is used,high-pressure gas for ejecting metal powder can be provided withoutincreasing the amount of gas consumption, and the efficiency of coatingmay be increased using plastic deformation of the metal powder heated toa temperature lower than a softening point thereof. The metal-coatedsteel plate of the present disclosure may have a coating layer nothaving pores owing to a plating layer formed between metal powderparticles, and thus the corrosion resistance of the metal-coated steelplate may be improved while guaranteeing functionality of the coatingpowder.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view illustrating an example structure of acoating layer formed according to the present disclosure.

FIG. 2 is a schematic view illustrating an example of an ejection deviceusable for performing a coating method of the present disclosure.

FIG. 3 is a schematic view illustrating another example of an ejectiondevice usable for performing the coating method of the presentdisclosure.

BEST MODE

Exemplary embodiments of the present disclosure will now be described indetail with reference to the accompanying drawings. The disclosure may,however, be exemplified in many different forms and should not beconstrued as being limited to the specific embodiments set forth herein.

The present disclosure provides a coating technique for maximizing thefunctionality of a metal coating layer by forming the metal coatinglayer on a steel plate without pores using a metal plating layer formedin the metal coating layer and/or between surface metal powder particlesof the metal coating layer, and a steel plate surface-treated using thecoating technique.

Steel plates to which a method for coating a steel plate with a metal isapplicable according to the present disclosure are not particularlylimited. However, the metal coating method of the present disclosure maybe applied to steel plates selected from the group consisting ofhot-rolled steel plates, cold-rolled steel plates, cold-rolled annealedsteel plates, galvanized steel plates, zinc-based alloy plated steelplates, and aluminum-based plated steel plates.

According to the present disclosure, the method for coating a steelplate with a metal includes: heating a first metal powder to atemperature equal to higher than room temperature but lower than asoftening point; heating a gas to a temperature of 200° C. to 600° C.;vacuum-ejecting the heated metal powder together with the heated gas toform a porous first metal coating layer; and forming a plating layer ofa second metal in gaps between powder particles of the first metalcoating layer.

That is, in the metal coating method of the present disclosure, acoating structure is formed by mixing a metal powder and a gas heated toproper temperatures, and ejecting the metal powder carried by the gas ina low-temperature, low-pressure atmosphere. According to the presentdisclosure, since the first metal powder is vacuum-ejected to the steelplate, an anchoring layer 8 may be formed on an interface with the steelplate as shown in FIG. 1.

Here, room temperature refers to a temperature ranging from about 15° C.to about 25° C.

In addition, according to the present disclosure, since the inside of avacuum body 100 into which the powder carried by the gas is ejected ismaintained in a low-temperature, low-pressure state, the gas may beejected by a high pressure difference between the carrier gas and acoating portion having a boundary at a nozzle ejection hole withoutincreasing the consumption of gas. Furthermore, since the vacuum body100 is maintained at a low temperature, even in the case that the gascarrying the powder is ejected, an increase in the internal pressure ofthe vacuum body 100 is prevented, and thus the powder may be stablyejected.

In the process of heating the powder of the first metal to a temperatureequal to or higher than room temperature but lower than the softeningpoint, the first metal may include at least one metal selected from thegroup consisting of copper (Cu), aluminum (Al), zinc (Zn), iron (Fe),nickel (Ni), chromium (Cr), molybdenum (Mo), titanium (Ti), cobalt (Co),manganese (Mn), tungsten (W), zirconium (Zr), and tin (Sn). However, thefirst metal is not limited thereto. The first metal may be at least oneof the listed metals, an alloy of at least two of the listed metals, oran alloy including at least one of the listed metals. For example,powder of stainless steel may be used. Powder of an Fe-based metal suchas 200 series, 300 series, or 400 series stainless steels may be used.In addition, powder of a high-strength alloy may also be used.Therefore, the softening point may vary according to the first metal.

In addition, according to the present disclosure, preferably, the firstmetal powder may have an aspect ratio (long-axis length/short-axislength)) of less than 2.

For example, the temperature at which the process of heating the firstmetal powder is performed may range from room temperature to 900° C. ifthe first metal powder is stainless steel powder.

If the temperature at which the process of heating the first metalpowder is performed is lower than room temperature, plastic deformationcoating may not smoothly occur. However, this may be overcome byadditionally heating the carrier gas. If the temperature at which theprocess of heating the first metal powder is performed is higher thanthe softening point, and the first metal powder has a high meltingpoint, the steel plate may be damaged, and manufacturing costs mayincrease.

The first metal powder may preferably have an average particle sizewithin the range of 1 μm to 20 μm, and more preferably within the rangeof 1 μm to 10 μm. If the average particle size of the first metal powderis less than 1 μm, manufacturing costs may increase because of highpowdering costs. Conversely, if the average particle size of the firstmetal powder is greater than 20 μm, it is difficult to form a densepowder coating layer because the size of pores between particles of thepowder coating layer is large, and gas consumption increases becauseimpact energy necessary for coating the steel plate with the first metalpowder increases and thus it is necessary to use the gas at a higherpressure.

In addition, the process of heating the gas is performed separately fromthe process of heating the first metal powder, and more particularly,the gas may preferably heated to a temperature of 200° C. to 600° C. andmore preferably, to a temperature of 200° to 500° C. If the temperatureis less than 200° C., a sufficient gas pressure is not guaranteed.Conversely, if the temperature is greater than 600° C., the steel platemay be damaged because the ejection velocity of the powder may increase,or material bending and high manufacturing costs may be caused becauseof a high temperature.

Herein, the gas may have a density equal to or lower than that of air,and the gas may be at least one selected from the group consisting ofnitrogen (N₂), helium (He), and air. However, the gas is not limitedthereto. That is, although a low-density gas such as nitrogen (N₂) orhelium (He) may be used as the gas, dry air having relatively highdensity may also be used as the gas by considering factors such as theconsumption amount or price of the gas.

A higher powder temperature may be effective in increasing theefficiency of coating with metal powder by plastic deformation. However,in the present disclosure, the metal powder is heated to theabove-mentioned temperature, and the metal powder is mixed with the gasheated to a relative lower temperature and supplied at a large flowrate. Then, the mixture is ejected, thereby maximizing the plasticstrain of the powder and realizing ejection at an optimized velocity.

Thereafter, the porous first metal coating layer is formed byvacuum-ejecting the heated metal powder together with the heated gas.

With reference to FIGS. 2 and 3, the metal coating method of the presentdisclosure will now be described in more detail together with a devicethat may be used to perform the method.

For example, the present disclosure may be implemented using a powderejection device 1 in which a steel plate being a coating target member 3may be provided in the vacuum body 100, and the powder may be ejectedtogether with the heated high-pressure gas carrying the powder onto thecoating target member 3 using a heating ejection unit 200 such that thepowder may be stacked on the coating target member 3 while undergoingplastic deformation.

The coating target member 3 is mounted on a member transfer device 3 ain the vacuum body 100 so as to be coated. Thereafter, the gas isprovided by a gas supply unit 220 and is heated by a gas heating unit230, and the powder is provided by a powder supply unit 210 and heatedby a powder heating unit 240. Then, the powder and the gas heated tohigh pressure are provided to a nozzle unit 250 and are ejected at ahigh velocity into the vacuum body 100 maintained at a vacuum state, andthus the powder may form a coating layer while being plasticallydeformed and stacked on the coating target member 3 provided in thevacuum body 100.

That is, according to the present disclosure, the gas and the powder areindividually heated before being ejected, and thus existing vacuumejection methods in which a high-pressure gas is provided by increasingthe flow rate of the gas and is then ejected may be improved so as toprovide a high-pressure gas for high-speed ejection of powder withoutincreasing the amount of gas consumption. In addition, the metal powderused as a coating material is heated to a particular temperature orhigher according to the kind of the metal powder, so as to increase theplastic strain of the metal powder and thus to facilitate stacking ofthe metal powder when the metal powder collides with the steel plate.

For example, the powder heating unit 240 may be provided to the powdersupply unit 210 for heating the powder. The powder is heated tofacilitate plastic deformation of the powder, and the powder heatingunit 240 may be controlled to have an operating temperature higher thanthat of the gas heating unit 230 so as to improve coating efficiency.That is, the powder heating unit 240 may be provided separately from thegas heating unit 230 to separately heat the gas and the powder and thusto obtain a powder temperature higher than a gas temperature. Inaddition, the powder heating unit 240 may also include a sensor S fortemperature measurement, and the sensor S may be connected to a controlunit C for heating temperature control.

To form a vacuum, the vacuum body 100 may include a chamber unit 110 inwhich the steel plate 3 is provided, and a vacuum unit 130 provided atthe chamber unit 110.

Here, the chamber unit 110 may be hermetically sealed to maintain avacuum formed by the vacuum unit 130. The transfer device 3 a on whichthe steel plate 3 is provided may also be provided in the chamber unit110.

Furthermore, in the present disclosure, the vacuum ejection maypreferably be performed at a pressure of 0.01 Torr to 20 Torr, and morepreferably at a pressure of 0.1 Torr to 15 Torr.

If the vacuum ejection is performed at a pressure less than 0.01 Torr,manufacturing costs increase to form a high-degree vacuum, and if thevacuum ejection is performed at a pressure greater than 20 Torr, asufficient powder ejection velocity may not be obtained because of anincrease in the pressure of a vacuum chamber.

For example, as illustrated in FIGS. 2 and 3, the vacuum unit 130 mayhave a function of forming a vacuum in the chamber unit 110, and to thisend, the vacuum unit 130 may include a vacuum pump 131, a powder filter132, and a cooler 133. That is, the vacuum unit 130 may have a functionof maintaining the inside of the chamber unit 110 in a low-degree vacuumstate ranging from 0.01 Torr to 20 Torr.

The vacuum body 100 may further include a cooling unit 120 to enablehigh-speed ejection by increasing a temperature difference between thevacuum body 100 and the heating ejection unit 200 to create a higherpressure difference.

That is, preferably, the vacuum ejection may be performed at atemperature of 10° C. to 200° C., and more preferably at a temperatureof 25° C. to 100° C. If the vacuum ejection is performed at atemperature less than 10° C., costs for maintaining the temperatureincreases, and if the vacuum ejection is performed at a temperaturegreater than 200° C., a sufficient pressure difference may not beobtained because of an increase in the pressure of the vacuum chamber.

That is, the cooling unit 120 may maintain the entire internal area ofthe chamber unit 110 at a low temperature, thereby increasing thepressure difference between the inside of the chamber unit 110 andsupplied gas for powder ejection at a higher velocity, and maintainingstable powder ejection by preventing an increase in the internalpressure of the chamber unit 110 even when the heating ejection unit 200(described later)) ejects the gas and powder.

Therefore, according to the present disclosure, the vacuum body 100 ofthe powder ejection device 1 may include the chamber unit 110 and thecooling unit 120 provided on the chamber unit 110 to maintain the insideof the chamber unit 110 at a low temperature. The cooling unit 120 maysurround outer surfaces of the chamber unit 110 in a dual structure asshown in the powder ejection device 1 shown in FIG. 2 to cool the entiresurface of the chamber unit 110, or may be provided as a cooling coil orcooling fins as shown in an ejection device 1, shown in FIG. 3.

As the gas and the first metal powder are heated and ejected into thevacuum body 100 at a higher velocity, the steel plate 3 being a coatingtarget member provided inside the vacuum body 100 may be coated with thefirst metal powder undergoing plastic deformation. To this end, theheating ejection unit 200 may include the powder supply unit 210, thegas supply unit 220, the gas heating unit 230, the powder heating unit240, the nozzle unit 250, etc.

The powder supply unit 210 supplies the powder to be ejected for coatingthe steel plate 3, and the powder may be heated by the powder heatingunit 240 and then may be supplied. In addition, the powder supply unit210 may adjust the supply amount of the powder and may receive some gasfrom a connection tube 223 a connected to a gas distributor 223 of thegas supply unit 220 such that powder stored in the powder supply unit210 may float in the gas and may receive driving force from the gaswhile the floating powder being transferred.

In addition, the gas supply unit 220 supplies high-pressure gas forejecting the powder at a high velocity. That is, since the powder isejected into the vacuum body 100 in a state in which the powder iscarried by the high-pressure gas ejected into the vacuum body 100, ifthe high-pressure gas is ejected at a high velocity, the powder may alsobe ejected at a high velocity. In addition, for high-speed ejection ofthe gas, the gas supply unit 220 may be maintained in a high-pressurestate, and in addition to this, the gas may be provided in ahigh-temperature, high-pressure state owing to heating by the gasheating unit 230. To this end, the gas supply unit 220 may include a gasstorage chamber 221, a gas transfer tube 222, the gas distributor 223, adehumidifier 224, etc., and a sensor S for measuring temperature may beprovided in connection with the control unit C so as to control thetemperature of heating by the gas heating unit 230.

The temperatures and velocities of gas and powder are key factorsdetermining the velocity of ejection and may be properly set accordingto the material of the metal powder. If the temperature or velocity ofthe gas is excessively low, when the metal powder collides with thesteel plate, sufficient impact energy for coating may not be obtained.Conversely, if the temperature or velocity of the gas is excessivelyhigh, etching rather than coating may occur, or the powder may not bestacked but may bounce off the steel plate after collision with thesteel plate.

That is, proper impact energy is necessary for coating the steel platewith the metal powder, and to this end, the temperature and velocityconditions of the gas and the powder are key factors. Under optimizedconditions, high impact energy may induce metallic bonding betweeninterfaces of the steel plate and the metal coating layer; anintermetallic layer may be formed of components of the steel plate andthe coating powder material; initial collision particles may dig intothe steel plate and form an anchoring layer owing to high impact energy;or at least two or all of these structures may be formed. In moredetail, if impact energy is low, the formation of an anchoring layer andstacking may occur even in the case that metallic bonding or theformation of an intermetallic layer does not occur. As impact energyincreases, metallic bonding occurs together with the formation of ananchoring layer, and an intermetallic layer may be formed if the steelplate and the powder have different components. In addition, if impactenergy is low, adhesion may be somewhat low. However, a heat treatmentprocess (described later) may be performed to induce metallic bondingwhich guarantees adhesion.

As described above, owing to the metallic bonding, the intermetalliclayer, and the anchoring layer between the steel plate and the firstmetal coating layer, strong adhesion may be obtained between the steelplate and the first metal coating layer. In addition, metallic bondingor an intermetallic layer involving plastic deformation may be presenteven between particles of the coating layer.

Through these processes, the metal powder may be ejected to the steelplate to form the metal coating layer with high coating efficiency.Although coating efficiency is high in this case, most powder particlesmay participate in coating the steel plate while colliding with thesteel plate in a state in which the powder particles maintain theirshapes with slight deformation, and due to this, pores may be formed inthe coating layer, thereby causing problems such as low corrosionresistance.

According to the present disclosure, preferably, the first metal powdermay have an aspect ratio (long-axis length/short-axis length)) of lessthan 2.

Therefore, according to the present disclosure, the process of formingthe second metal plating layer is performed.

That is, according to the present disclosure, an additional metal layeris formed between the metal powder particles by plating a surfaceregion, an inner region, or both regions of the metal coating layer toprovide a final pore-free coating layer, thereby preventing permeationof corrosion factors and maximizing the functionality of the coatingmaterial.

In this case, the second metal may include at least one selected fromthe group consisting of zinc (Zn), nickel (Ni), tin (Sn), copper (Cu),and chromium (Cr). However, the second metal is not limited thereto. Forexample, the second metal may be one of the listed metals, an alloy ofat least two of the listed metals, or an alloy including at least one ofthe listed metals.

In addition, the process of forming the plating layer may be performedby an electroplating method or an electroless plating method.

The is, the steel plate on which the metal coating layer is formed maybe plated with an additional plating layer by an electroplating methodor an electroless plating method to fill pores between powder particlesof the metal coating layer, thereby removing pores of the metal coatinglayer.

FIG. 1 is a schematic view illustrating a structure in which anadditional metal layer is formed by plating gaps between metal powderparticles of a metal coating layer and a surface region of the metalcoating layer. In another example, a plating layer may be formed mainlyon pores between metal powder particles inside the coating layer whilesuppressing the surface region of the coating layer from being plated.In the latter case, an inhibitor may be included in a plating solution,and the metal layer may additionally only be formed in the pores of themetal coating layer.

In this case, the inhibitor is not particularly limited. An inhibitorgenerally used in an electroplating method or an electroless platingmethod may be used as long as the inhibitor optimizes characteristics ofthe metal coating layer determined by the kind of metal and the size ofpowder of the metal coating layer of the present disclosure. Forexample, a surfactant such as a polyol-based or amine-based organiccompound surfactant may be used.

In addition, according to the present disclosure, a process of polishingthe second metal plating layer may be additionally included.

If the polishing process is performed, pores in a surface region may beminimized, and hair lines or metallic texture may be imparted to thesurface of the metal coating layer to improve appearance. Owing tofriction during the polishing process, surface pores may be closed, andowing to metal texture such as hair lines formed through the polishingprocess, the value of products may also be improved.

In addition, in the coating method of the present disclosure, a heattreatment process may be additionally performed at a temperature of 200°C. to 1000° C., and it may be more preferable that the heat treatmenttemperature be within the range of 300° C. to 850° C.

The temperature of the additional heat treatment process may be lowerthan the melting point of the metal or alloy of the metal coating layer,and if the steel plate is a plated steel plate, the heat treatmentprocess may be performed at a low temperature for a long period of timeby considering the melting point of a plating layer and the alloyingtemperature of the plating layer.

In addition, a heat treatment method such as a laser or plasma heatingmethod may be used to have heat treatment effects only on the coatinglayer while minimizing the influence of heat on the steel plate.

As described above, owing to the additional heat treatment process,pores in the metal coating layer may be further minimized, and adhesionmay be secured between the steel plate and the metal coating layer,between powder particles of the metal coating layer, and between metalpowder particles and the plating layer, thereby improving workabilitytogether with corrosion resistance.

The reason for this is that sintering occurs at interfaces during theadditional heat treatment. In addition, although dislocations occur incrystal grains due to plastic deformation of powder particles during thecoating process, the heat treatment removes the dislocations, andcrystal grains of the powder particles recrystallize to a size less thanthe original average size D50 of the powder particles. Thus, workabilityimproves compared to the case in which the metal coating layer is notheat treated.

In this case, different metals may form intermetallic layers at aninterface between the metal power particles and at an interface betweenthe base steel plate and the metal coating layer.

The additional heat treatment process may be performed before or afterthe polishing process. That is, the order of the processes is notlimited.

The present disclosure provides a metal-coated steel plate manufacturedby the above-described method for coating a steel plate of the presentdisclosure.

In more detail, the metal-coated steel plate of the present disclosureincludes: a steel plate; a porous first metal coating layer formed on atleast one surface of the steel plate using a first metal powder; and aplating layer of a second metal formed in gaps between metal powderparticles of the first metal coating layer.

Referring to FIG. 1, a metal-coated steel plate 2 includes: a firstmetal coating layer 4 formed on a steel plate or a plated steel plate 3by ejecting a first metal powder onto the steel plate 3; and a secondmetal plating layer 6 formed in gaps between metal powder particles 5 ofthe first metal coating layer 4. That is, the metal-coated steel plate 2has a pore-free coating layer 4 a.

In this case, the second metal plating layer may be formed in pores ofthe first metal coating layer and/or on a surface region of the firstmetal coating layer. Therefore, a coating layer free of pores is finallyprovided, thereby guaranteeing corrosion resistance because corrosionfactors are prevented from reaching the steel plate, and maximizing thefunctionality of the metal of the coating layer.

In addition, according to the present disclosure, the porous first metalcoating layer is formed through a vacuum ejection process, and thus thesize of crystal grains of the first metal powder is less than theaverage size D50 of original powder particles.

In addition, an intermetallic layer is present at interface between thefirst metal powder particles and the second metal plating layer formedbetween the first metal powder particles, and metallic bonding, ananchoring layer 8, and an intermetallic layer may be formed on aninterface between the steel plate and the first metal coating layer.

The first metal may include at least one metal selected from the groupconsisting of copper (Cu), aluminum (Al), zinc (Zn), iron (Fe), nickel(Ni), chromium (Cr), molybdenum (Mo), titanium (Ti), cobalt (Co),manganese (Mn), tungsten (W), zirconium (Zr), and tin (Sn). However, thefirst metal is not limited thereto. The first metal may be at least oneof the listed metals, an alloy of at least two of the listed metals, oran alloy including at least one of the listed metals. For example,powder of stainless steel may be used. Powder of an Fe-based metal suchas 200 series, 300 series, or 400 series stainless steels may be used.In addition, powder of a high-strength alloy may also be used.Therefore, the softening point may vary according to the first metal.

The first metal powder may be powder of a single metal having an averageparticle size preferably within the range of 1 μm to 20 μm, morepreferably within the range of 3 μm to 10 μm, and even more preferablywithin the range of 5 μm to 10 μm. If the average particle size of thefirst metal powder is less than 1 μm, manufacturing costs may increasebecause of high powdering costs. Conversely, if the average particlesize of the first metal powder is greater than 20 μm, it is difficult toform a dense powder coating layer because the size of pores betweenparticles of the powder coating layer is large, and gas consumptionincreases because impact energy necessary for coating the steel platewith the first metal powder increases and thus it is necessary to usegas at a higher pressure.

In this case, the second metal may include at least one selected fromthe group consisting of zinc (Zn), nickel (Ni), tin (Sn), copper (Cu),and chromium (Cr). However, the second metal is not limited thereto. Forexample, the second metal may be one of the listed metals, an alloy ofat least two of the listed metals, or an alloy including at least one ofthe listed metals.

Hereinafter, the present disclosure will be described more specificallythrough examples. The following examples are for illustrative purposesonly and are not intended to limit the scope of the present invention.

MODE FOR INVENTION Examples

1. Experiment for Checking Temperature-Dependent Variations in CoatingLayer During Coating Process

A cold-rolled steel plate was used as a coating target object to becoated, and stainless steel powder was used as a coating material. Theaverage particle size D50 of the powder was 5 μm, and the particle sizeof the powder followed a normal distribution within the range of 1 μm to10 μm.

A coating experiment was performed using the coating device shown inFIG. 2 by filling the powder supply unit 210 with the powder and settingcoating conditions as follows: an initial pressure of the vacuum body100 was set to 5×0.01 Torr, and a gas pressure before ejection through anozzle was set to 800 Torr. At that time, dry air was used as gas, andthe flow rate was set to be 30 L/min at a powder transfer tube 211 and200 L/min at the gas transfer tube 222. In addition, a cylinder nozzlehaving a throat size of 0.8 mm×100 mm was used as the nozzle unit 250 insuch a manner that the nozzle unit 250 was fixed at a distance of 10 mmaway from the coating target material, and coating was performed whilemoving the coating target material left and right twice at a velocity of10 mm/sec.

The powder heating unit 240 and the gas heating unit 230 were operatedto adjust the temperatures of the powder transfer tube 211 and the gastransfer tube 222 to values shown in Table 1 below during the coatingexperiment.

The thickness of a coating layer of the cold-rolled steel plate being acoating target member was measured by cross-sectional element analysisof chromium (Cr) using a scanning electron microscope (SEM), and averagevalues of the measured values are shown in Table 1 below according tocoating conditions.

TABLE 1 Temperature of Temperature of Thickness of powder transfer gastransfer coating layer No tube (° C.) tube (° C.) (μm) Comparative Roomtemperature Room temperature less than 0.2 Example 1 coating ComparativeRoom temperature 150 2.5 Example 2 Example 1 Room temperature 200 10Example 2 Room temperature 600 29 Example 3 300 600 34 Example 4 600 60053 Example 5 800 600 86

As shown in Table 1 above, coating scarcely occurred in ComparativeExample 1 performed under room temperature conditions, and the thicknessof a coating layer increased as the temperature of the gas increased asshown in Comparative Example 2 (the size of particles followed a normaldistribution within the range of 1 μm to 10 μm), Example 1, and Example2. However, in Comparative Example 2, a structure not having pores wasobtained with low coating efficiency, and thus Comparative Example 2 isnot useful. In Examples 1 to 5, pores were formed.

The reason for these results is that the pressure of the gas increasesas the temperature of the gas increases, and the ejection velocity ofpowder increases as the pressure difference between the high-pressuregas and the inside of the vacuum body 100 increases.

In addition, it could be understood that the thickness of the coatinglayer increased owing to heating of the powder. Therefore, the plasticstrain of the metal powder could be maximized by heating the metalpowder, and thus the efficiency of coating could be markedly increasedwhen compared to Comparative Example 1.

2. Experiment for Checking Properties of Coating Layer According toCoating Processes

The same base steel plate and coating conditions as those used inExperiment 1 were used. In detail, the same temperature conditions asthose in Example 4 shown in Table were used, but samples were preparedby setting the average particle size of powder to be 5 μm and thecoating thickness to be about 25 μm.

The samples prepared in this manner were additionally subjected toprocesses such as an electroplating process, a heat treatment process,or a polishing process as shown in Table 2 below, and when a pluralityof subsequent processes were performed, the processes were performed inthe order of an electroplating process, a heat treatment process, and apolishing process.

The electroplating process was performed to plate a metal powder coatinglayer with nickel (Ni) using a plating solution to which an inhibitorwas added in a very small amount under the conditions of a currentdensity of 20 A/dm², a plating solution temperature of 50° C., and aplating weight of 2 g/m².

The heat treatment process was performed at 850° C. for 5 minutes undera reducing atmosphere, and the polishing process was performed usinggeneral sand paper until a surface region was removed by about 2 μm to 5μm.

The corrosion resistance and workability of the samples prepared asdescribed above were measured, and results thereof are shown in Table 2below.

Corrosion resistance was measured through a salt spray test by measuringthe time taken until an area of red rust reached 5% of the total area,75 mm×150 mm, of each sample.

Workability was measured through a bending test by checking theformation of cracks in a portion bent to 90° C. with a radius ofcurvature of 3 mm by using an optical microscope. In Table 2 below, “X”denotes that cracking occurred, and “O” denotes that cracking did notoccur.

TABLE 2 Salt spray test (red rust 5% Electro- Heat occurrence Bending Noplating treatment Polishing time) test Comparative not not not less than24 x Example 3 performed performed performed hours Comparative notperformed not 24 to 48 ∘ Example 4 performed performed hours Comparativenot not performed 96 to 120 x Example 5 performed performed hoursComparative not performed performed 96 to 120 ∘ Example 6 performedhours Example 6 performed not not 120 to 168 x performed performed hoursExample 7 performed performed not 240 hours or ∘ performed longerExample 8 performed not performed 240 hours or x performed longerExample 9 performed performed performed 240 hours or ∘ longer

In the case of Comparative Examples 3 to 6 having pores in metal coatinglayers, corrosion resistance could be increased to some degree throughthe heat treatment process or polishing process even in the case thatthe metal coating layers did not include a metal in addition to themetal powder. However, the corrosion resistance and functionality of theSTS powder coating layer were not sufficient.

In addition, as shown in Example 6, the functionality of the coatinglayer was more effectively shown when an additional metal is includedbetween coating powder particles, and as shown in Examples 7 to 9, thecharacteristics of the coating layer could be further improved byadditionally performing heat treatment and polishing.

While exemplary embodiments have been shown and described above, thescope of the present disclosure is not limited thereto, and it will beapparent to those skilled in the art that modifications and variationscould be made without departing from the scope of the present inventionas defined by the appended claims.

[Reference numerals] 1: POWDER EJECTION DEVICE 2: METAL-COATED STEELPLATE 3: COATING TARGET MATERIAL (SUPPLY PIPE OR PLATED STEEL PLATE) 4:METAL COATING LAYER 4A: PORE-FREE COATING LAYER 5: FIRST METAL POWDERPARTICLES 6: SECOND METAL 7: PORES 8: ANCHORING LAYER 100: VACUUM BODY110: CHAMBER UNIT 120: COOLING UNIT 130: VACUUM UNIT 131: VACUUM PUMP132: POWDER FILTER 133: COOLER 200: HEATING EJECTION UNIT 210: POWDERSUPPLY UNIT 211: POWDER TRANSFER TUBE 220: GAS SUPPLY UNIT 221: GASSTORAGE CHAMBER 222: GAS TRANSFER TUBE 223: GAS DISTRIBUTOR 223A:CONNECTION TUBE 224: DEHUMIDIFIER 230: GAS HEATING UNIT 240: POWDERHEATING UNIT 250: NOZZLE UNIT

1. A method for coating a steel plate with a metal, the methodcomprising: heating a first metal powder to a temperature equal to, orhigher than, room temperature but lower than a softening temperature;heating a gas to a temperature of 200° C. to 600° C.; vacuum-ejectingthe first metal powder, having been heated, together with the heated gasto form a porous first metal coating layer; and forming a plating layerof a second metal in gaps between powder particles of the first metalcoating layer.
 2. The method of claim 1, wherein the first metalcomprises at least one metal selected from the group consisting ofcopper (Cu), aluminum (Al), zinc (Zn), iron (Fe), nickel (Ni), chromium(Cr), molybdenum (Mo), titanium (Ti), cobalt (Co), manganese (Mn),tungsten (W), zirconium (Zr), and tin (Sn).
 3. The method of claim 1,wherein the first metal powder has an average particle size of 1 μm to20 μm.
 4. The method of claim 1, wherein the gas comprises at least onegas having a density equal to, or lower than the density of air which isselected from the group consisting of nitrogen (N₂), helium (He), andair.
 5. The method of claim 1, wherein the vacuum-ejecting is performedat a pressure of 0.01 Torr to 20 Torr.
 6. The method of claim 1, whereinthe vacuum-ejecting is performed at a temperature of 10° C. to 200° C.7. The method of claim 1, wherein the second metal comprises at leastone metal selected from the group consisting of zinc (Zn), nickel (Ni),tin (Sn), copper (Cu), and chromium (Cr).
 8. The method of claim 1,wherein the forming of the plating layer of the second metal isperformed by an electroplating method or an electroless plating method.9. The method of claim 1, further comprising polishing the plating layerof the second metal.
 10. The method of claim 1, further comprisingperforming a heat treatment process at a temperature of 200° C. to 1000°C. after the forming of the plating layer of the second metal.
 11. Ametal-coated steel plate manufactured by the method of claim
 1. 12. Ametal-coated steel plate comprising: a steel plate; a porous first metalcoating layer formed on at least one surface of the steel plate using afirst metal powder; and a plating layer of a second metal formed in gapsbetween particles of the first metal powder of the first metal coatinglayer.
 13. The metal-coated steel plate of claim 12, wherein the secondmetal plating layer is formed on a surface region of the first metalcoating layer and in pores of the first metal coating layer.
 14. Themetal-coated steel plate of claim 12, wherein an anchoring layer isformed on an interface between the steel plate and the first metalcoating layer.
 15. The metal-coated steel plate of claim 12, wherein thefirst metal comprises at least one metal selected from the groupconsisting of copper (Cu), aluminum (Al), zinc (Zn), iron (Fe), nickel(Ni), chromium (Cr), molybdenum (Mo), titanium (Ti), cobalt (Co),manganese (Mn), tungsten (W), zirconium (Zr), and tin (Sn).
 16. Themetal-coated steel plate of claim 12, wherein the first metal powder hasan average particle size of 1 μm to 20 μm.
 17. The metal-coated steelplate of claim 12, wherein the second metal comprises at least one metalselected from the group consisting of zinc (Zn), nickel (Ni), tin (Sn),copper (Cu), and chromium (Cr).